Alkaline reduction of hydrocarbonoxy silanes



United States Patent 3,122,539 ALKALINE REDUCTION 0F HYDRGCARBGNQXY SEANES John W. Ryan, Midland, ieh, assignor to Dow Corning Corporation, Midland, Mic a corporation of Michis n No Drawing. Filed Mar. 2, 1%1, Ser. No. 98,77? 4 Claims. (Cl. 269-4483) This invention relates to a method for reduction of lower alkoxy-l and phenoxyl radicals on silane silicon atmos to lower alkyl and phenyl radicals on silane silicon atoms by heating the silanes in a closed system with an alkali metal. This application is a continuation-impart of my copending application Serial Number 51,539, filed August 24, 1960, now abandoned.

In the preparation of hydrocarbon-substituted silanes by the direct process the product is a mixture of mono-, diand tri-hydrocarbon-substituted silanes. Since the organopolysiloxanes prepared from the diand tri-hydrocarbon-substituted silanes are presently more commercially desirable than the organopolysiloxanes prepared from mono-hydrocarbon-substituted sil anes, there has developed a need for some method of converting monohydrocarbon-substituted silanes to diand tri-hydrocarbon-substituted silanes. Various meLhods of disproportionation, i.e. redistribution of silicon-bonded hydrocarbon radicals, have been developed. However, no other feasible type of method has been available to accomplish the desired conversion.

One of the objects of this invention is to provide a method of producing diand tri-hydrocarbon-substituted silanes from mono-hydrocarboil-substituted and unsubstituted silanes. Another object of this invention is to provide a method of reducing silicon-bonded methoxyl and phenoxyl radicals to silicon bonded methyl and phenyl radicals respectively. Another object of this invention is to provide a method of preparing silanes havboth alltyl and phenyl radicals attached to each silicon atom from silanes having only alkyl radicals attached to each silicon atom. 'lhese objects as well as others which are apparent from the following description are satisfied by this invention.

This invention relates to the method which comprises heating at a temperature above 150 C. a mixture of (A) silanes of the formula R Si(OR') in which each R is a monovalent hydrocarbon radical free of aliphatic unsaturation, each R is a radical independently selected from the group consisting of the methyl radical and the phenyl radical and m is a positive integer ranging in value from 2 to 4 and from about 0.1 to about percent by weight based on the weight of A of (B) an alkali metal whereby silanes other than A are produced having the formula R.-, Si(OR') in which R and R are as defined above, 22 is a positive integer ranging in value from 1 to 3 and the average value of n is less than the average value of in.

Component A in the method of this invention consists of silanes of the general formula R.-, Si(OR) in which each R can be any monovalent hydrocarbon radical free of aliphatic unsaturation, each R can be a methyl or phenyl radical and m can be 2, 3 or 4. More specifically, each R can be, for example, any dkyl radical such as the methyl, ethyl, isopropyl, butyl, t-butyl, Z-ethylhexyl, dodecyl, octadecyl and myricyl radicals; any cycloallryl radical such as the cyclopentyl and cyclohexyl radicals; any aryl radical such as the cyclopentyl and cyclohexyl radicals; any aryl radical such as the phenyl, Xenyl and naphthyl radicals; any aralkyl radical such as the benzyl and xylyl radicals or any alkaryl radical such as the tolyl and dimethylphenyl radicals. Examples of typical silanes amass Patented Feb. 25, P964 which can be employed in the method of this invention ininclude:

Si B 5) 4 CH Si( OCH 3 5 9 GC6HS J a C l-1 5i (OCH s s s a) 3 These examples merely illustrate the variety of silanes which can be employed in the method of this invention.

Component B in the method of this invention is any alkali metal such as sodium, potassium, lithium or cesium.

The method of this invention involves in some order mixing components A and B and heating them at a temperature of at least 150 C. The reaction temperature depends primarily on the R radicals present in the system. Phenoxyl radical-s can be reduced to phenyl radicals at temperatures of at least 150 C., preferably in the range of 220 C. to 300 C. Methoxyl radicals can be reduced to methyl radicals only by heating to temperatures greater than 200 C., prefera ly from about 230 C. to about 270 C. There is no critical maximum temperature except the decomposition temperature of the R radicals, OR' radicals or compounds in the system. Although this method is operative in the vapor state, it is preferable to operate in a liquid state. This can be done by using a closed system when temperatures above the boiling point of any reactant are employed and by staying below critical temperatures, e.g. 282 C. for methyltrimethoxysilane.

The ratio of B to A can vary a great deal due to the relative activities of the various alkali metals. However, more than about 20 percent by weight of B based on the weight of A is unnecessary although the presence of excess B is not detrimental generally depending on time and temperature conditions. Likewise as little as about 0.1 percent by weight of B based on the weight of A can be used under proper "conditions of time and temperature. However, at least 1.0 percent by Weight of B based on the Weight of A is preferred.

The time of heating in the method of this invention depends on the temperature, the composition of compo nent A, the amount and activity of B, the desired prodnets and the desired yield. For example, the method of this invention produces from monomethyltrimethoaysilane some dirnethyldimethoxysilane in less than an hour at 270 C. with 2.5 percent by weight of sodium based on the \wei it of the monomethyltrimethoxysilane. On the other hand this method can operate over hours with 1.0 percent by weight of lithium producing both :dimethyldimethoxysilane and trimethyl-methoxysilane. Since in the reduction of the methoxyl radicals t e alkali metal is consumed in the formation Olf vaiorus basic compounds such as alkali metal methoxides, oxides and silvanolates, there is also a general migration of methyl radicals as Well as any ethyl and phenyl radicals from one silicon atom to another as described in my cooending application Serial No. 98,778 entitled Alkaline Rearrangement of Hydrocarbon-Substituted Silanes filed concurrently herewith. However, this migration of radicals does not interfere apparently with the reduction reaction.

The method of this invention produces products diiferout from the reactants and having the general formula R Si(OR) in which R and R are as defined above and n is l, 2 or 3. The average value of n is less than the average value of m in the starting material R f-li(O-R) since some -OR' radicals are removed from the system by reduction. In specific cases methyltrimethoxysilane produces dimethyldimethoxysilane and trimethylmethoxysilane, i.e. silanes of the formula (CI-l .Si(OCl-I in which r can be 2 or 3, or methyltriphenoxysilane produces methylphenyldiphenoxysilane or methyldiphenylphenoxysilane, i.e. silanes of the formula in which .9 can be 1 or 2.

The following examples show some of the possible variations in time, temperature, silanes, alkali metals, proportions and products. These exarnples are merely illustrative and are not intended to limit this invention the scope of which is properly delineated in the claims. The symbols Me and Ph represent the methyl and phenyl radicals respectively. All quantitative measurements are in parts by weight.

EXAMPLE 1 In each of the followin runs 100 parts by weight of methyltrimethoxysilane were mixed with the amount of alkali metal compound shown in an autoclave which was sealed and heated at the temperature and for the time shown. The liquid portion of the reaction product was distilled to separate trimethylmethoxysilane (13.1. 555 C.), dimethyldimethoxysilane (HP. 802 C.), methyltrimethoxy-silane (3P. 102 C.) and dimethylether (B.P. 21.6 C.).

The results were as follows:

are mixed and heated in a closed system for 16 hours at 270 C. and the resulting liquid is cooled and distilled,

MePhSi(OPh) and MePh SiOPh are produced.

EXAMPLE 6 When the following silanes are substituted for the Si(OMe) in Example 3, the following compounds are produced.

That which is claimed is:

1. The method which consists in heating at a temperature above 150 C. a mixture of (A) silanes of the formula R Si(OR) in which each R is a monovalent hydrocarbon radical free of aliphatic unsaturatio-n, each R is a radical independently selected from the group consisting of the methyl radical and the phenyl radical and m is a positive integer ranging in value from 2 to 4 and from about 0.1 to about percent by weight based on the weight of A of (B) an alkali metal whereby silanes other than A are produced having the formula in which R and R are as defined above, n is a positive integer ranging in value from 1 to 3 and the average value of n is less than the average value of m.

2. The method which consists in heating in a closed system at a temperature above 200 C. a mixture of (A) Table Wt. M01 Percent of Me in A present in product Percent Temp Time as- Cornponent B Basekd C.) (hr) on i McaSiOh/Ie MezSi(OMe)z MeSi(OMe)a N a 12. 9 230 16 47 as 19 2. 5 250 6. O 7 34 5o 2. 6 240 S7 6 1. 7 250 15 2 36 58 6. 8 270 4. 3 16 49 26 2. O 270 23 4 6 81 3. 5 270 22 6 38 46 EXAMPLE 2 methyltrimethoxysilane with from about 0.1 to about 20 491 parts of Me Si(0?h) and 35 parts of sodium were mixed and heated in a closed system for 16 hours at 275 to 277 C. A liquid product resulted containing as one component PhMe SiOPh.

EXAMPLE 3 400 parts of Si(OMe) and 53 parts of sodium were mixed and heated 2 hours at 220 C. and 18 hours at 230 C. in a closed system. The products included Me Si(OMe) and MeSi(OMe) EXAMPLE 4 400 parts of n-propyltrimethoxysilane and 28.5 parts of sodium were mixed and heated in a closed system for 20 hours at 278 C. The products included percent by weight based on the weight of A of (B) an alkali metal whereby silanes are produced having the formula (CI-l Si(OCI-I in which r is a positive integer ranging in value from 2 to 3.

3. The method of claim 2 wherein the heating temperature ranges from about 230 C. to about 270 C.

4. The method which comprises heating at a temperature above 220 C. a mixture of (A) methyltriphenoxysilane with from about 0.1 to about 20 percent by weight based on the Weight of A of (B) an alkali metal whereby silanes are produced having the formula 3) e 5)s a 5) 3-5 in which s is a positive integer ranging in value from 1 to 2.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,444 Taylor June 28, 1949 

1. THE METHOD WHICH CONSISTS IN HEATING AT A TEMPERATURE ABOVE 150*C. A MIXTURE OF (A) SILANES OF THE FORMULA R4-MSI(OR'')M IN WHICH EACH R IS A MONOVALENT HYDROCARBON RADICAL FREE OF ALIPHATIC UNSATURATION, EACH R'' IS A RADICAL INDEPENDENTLY SELECTED FROM THE GROUP CONSISTING OF THE METHYL RADICAL AND THE PHENYL RADICAL AND M IS A POSITIVE INTEGER RANGING IN VALUE FROM 2 TO 4 AND FROM ABOUT 0.1 TO ABOUT 20 PERCENT BY WEIGHT BASED ON THE WEIGHT OF A OF (B) AN ALKALI METAL WHEREBY SILANES OTHER THAN A ARE PRODUCED HAVING THE FORMULA 